\/ 


Circular   No    7.  Second  Serics. 


United  Stales  Department  of  Agriculture, 


DIVISION    OK   ENTOMOLOGY. 


THE  PEAR  TREK  PSYLLA. 

ilia  pyricola  Foerett  i      « , 

V  ii  overwhelming  invasion  of  the  pea  lyllaTtn-thi 

hi  the  largest  pear  orchards  in  Maryland,  together  with 
Virginia  and  New  Jersey  in  the  same  year,  gives  promim 
had  nol  previously  been  reported  Bouth  ol  New  York,  although  known  to  extend 


18Jj:SI 


Fn.  1. -Pear-tree  PsylU    A.lult  female     Natoral  riie  indlcafa  oe,    (Original.) 

■  l  a-  far  aa  Michigan  and  to  occur  generally  in  the  New  England  States. 

'"   Vl,u  northern   range,  its   sodden  appearance  in  enormous 

number*   BO    tar    small    was    a    matter    ol    considerable    surprise,    and     careful 

iminations   of  the   work  of  the    insect    and    experiments   with  remedies   were 

made. 

The  pear-tree  Peylla  (fig.  I)  is  supposed  to  have  been  imported  into  Connec- 
ticut about  1832  from  Europe,  where  this  and  one  or  two  other  spedes  are  well- 
known  pear  enemies.  It  is  one  of  the  true  bags  of  the  order  Ilomoptera,  and 
^^^  family,  the  Psyllid.-e,  is  intermedial-  between  or  connects  the  scale  insects 
|     K""1  t,u>  plant-lice  on  the  one  hand  with  thi  and   larger  plain 

^^^•be  other.     The    I'syllidie  are  commonlv   known   as  the  jumping  plant-lice    on 

r ' ' 


NATURE   OF   THE   INJURY. 

The  pear-tree  Psylla  has  hitherto  been  by  no  means  a  common  insect,  and 
few  pear  growers  are  familiar  with  it.  The  insect,  even  in  the  later  stages,  is 
small  and  easily  overlooked,  but  the  effects  of  its  presence  upon  the  trees  are 
startling  enough,  as  seen  in  the  falling  of  the  leaves  and  fruit,  the  latter  before 
it  is  half  grown,  but  chiefly  in  the  enormous  secretion  of  honeydew  by  the  larva' 
and  nymphs.  One  who  has  not  witnessed  this  sight  gives  credence  with  diffi- 
culty to  the  reports  of  the  amount  of  this  liquid  constantly  being  secreted.  Dur- 
ing the  height  of  the  invasion  in  Maryland  the  waterlike  fluid  or  honeydew  was 
reported  not  only  to  have  covered  the  leaves  and  twigs,  but  to  have  fairly  rained 
from  the  leaves,  and,  running  down  the  trunks,  extended  in  a  discolored  circle 
for  from  6  to  8  inches  outward  around  the  baee  of  the  trees.  During  cultivation 
the  horses  used  became  so  drenched  with  the  sticky  6ubstance  that  it  became 
necessary  to  wash  it  off  with  sponges,  the  currycomb  being  useless.  The  weak- 
ened trees  lost  much  of  their  fruit,  the  leaves  were  blackened  and  fell  in  great 
numbers,  and  the  bodies  of  the  trees  appeared  as  if  they  had  been  smoked.1 

On  July  20,  when  first  seen  by  the  writer,  the  leaves,  limbs,  and  trunks  were 
blackened  by  the  growth  in  the  sweetish  liquid  of  the  smoky  fungus,  Fumago 
salicina;  and  in  the  falling  of  the  foliage  and  the  diseased  and  smoky-looking 
fruit  a  startling  picture  of  disaster  was  presented.  The  leaves  were  scarcely  at 
all  yellowed,  but  were  covered  with  dead  and  dry  patches  or  spots,  sometimes 
investing  almost  the  entire  leaf,  giving  an  appearance  which  might  easily  be 
mistaken  for  some  fungous  attack.  This  seems  to  be  due  not  directly  to  the 
extraction  of  the  plant  juices  by  the  insects,  but  rather  to  the  sun-scalding 
resulting  from  the  collection  of  the  honeydew  on  the  leaves  in  large  drops.  The 
Psylla  was  distributed  over  the  entire  orchard  of  upwards  of  100  acres,  but  was 
much  more  abundant  in  the  plats  of  older  trees.  The  young  orchards,  perhaps 
amounting  to  one-third  of  the  entire  tract,  were  in  vigorous  condition  and  had 
not  been  seriously  affected.  This  was  noticeably  the  case  with  the  Kieffer, 
Buffon,  Le  Conte,  and  Standard  Lawrence.  The  Dwarf  Lawrence,  on  the  con- 
trary, was  badly  injured,  and,  with  the  Old  Duchess  and  Bartlett  trees,  seemed 
to  have  suffered  the  most. 

OTHER  OCCURRENCES  SOUTH  OK  NEW  YORK. 

The  presence  of  this  pest,  as  recorded  above,  is  not  the  first  instance  of  its 
occurrence  in  Maryland.  A  pear  orchard  about  8  miles  south  of  this  one  was 
also  very  badly  infested  in  the  summer  of  1891.  The  insect  appeared  during  that 
year  on  pear  trees  next  to  and  in  the  vicinity  of  the  house,  where  some  nursery 
stock  had  been  heeled-in  the  winter  previous.  Its  spread  was  confined  to  an 
area  of  3  or  4  acres,  which,  however,  was  so  thickly  infested  that  the  leaves  and 
fruit  fell,  and  the  trees  were  so  stunted  and  injured  that  they  ceased  bearing 
until  the  season  of  1894,  when  they  bore  a  fairly  good  crop.  Curiously  enough, 
however,  in  this  orchard  the  Psylla  disappeared  entirely  after  the  first  year  and 
has  not  again  put  in  an  appearance,  nor  did  it  occur  in  other  pear  orchards 
between  and  in  the  neighborhood  of  the  two  referred  to.  Similar  outbreaks  are 
reported  this  year  for  the  first  time  in  New  Jersey  by  Prof.  John  B.  Smith,  with 
evidences  of  the  same  source  of  infestation,  and  about  the  middle  of  October  it 
was  found  in  Charlottesville,  Va.,  by  Mr.  D.  W.  Coquillett.  These  records  evi- 
dence an  unfortunate  tendency  of  the  insect  to  spread  southward— a  course 
which,  from  the  history  of  the  pest  during  the  sixty  years  of  its  occurrence  in 
this  country,  was  hardly  to  be  expected.  1 

1  Chester-town  (M.I.)  Transcript.  July  10.  1904. 


1 


Ml    I  IM.].    ()K     IS  I  ROD!   CI  H'N. 


I 


The  -- n . l . i « ■  1 1 1 1 .  —  and  severity  of  the  appearance  of  the  Psylla,  particularly  In 
the  Maryland  instances,  makei  the  question  ol  Its  introduction  one  ol  consider- 
able interest.  Upon  Inquiry  11  wu  developed  that  In  u  the  pear 
had  been  obtained  from  a  New  York  nursery  in  1800,  or  Jus)  at  the  time  when 
tin'  Psylla  appeared  in  Booh  extraordinary  onmbers  in  Wen  York  Btate;  and  it 
is  unquestionably  from  this  lonree  thai  the  Psylla  was  introduced.  The  young 
trees  secured  in  the  fall  "t  the  year  mentioned  were  nndonbtedly  Infested  with 
hibernating  Psyllas,  as  il  was  in  the  immediate  vicinity  of  the  point  where 
tin-  were  beeled  in  that  tin.  outbreaks  occurred.  In  one  case  tin'  insect  seemed 
t<>  have  gradually  increased  in  numbers,  reaching  a  destructive  abundance  in 
thr  summer  of  1894.  Tin-  entire  disappearance  ol  the  insect  after  the  first  year 
in  tlir  other  orchard  is  probably  to  be  explained  on  the  ground  of  Bome  local 
climatic  condition.  Sued  modifying  Influences  arc  not  unusual  in  the  peach 
licit  of  Maryland,  as  illustrated  by  the  fact  that  orchards  separated  by  only  a  few 

miles,   ami    with  the  same  c ditions  as  regards  s.>il   ami   variety   of   fruit,    will 

ingly  l>e  so  differently  affected  by 
\.-ry  local  cold  waves  or  storms  that  one 

will  be  barren  While  the  other  will  he  full 
of  fruit. 

or  -.  Kill  [ON    ami    LIFE    HISTORY. 

a  in  the  development  of  this 
insect  arc  the  egg,  the  larva,  the  nymph 
or  active  pupa,  and  the  adult  or  perfect, 
winded  insect,  rhe  egg  itig.  2,  a)  is 
orange-yellow  in  color  and  bo  minub 
to  he  almost  invisible  to  the  naked  eye. 

Its  peculiar  structure  is  indicated  in  the 

drawing— the  short  arm  serving  as  its 
attachment  to  the  leaf.  The  newly 
hatched    h\r\  a   is   somewhat   larger  than 

the  egg  and  yellow  in  color,  with  crimson  eyes,  and  has  the  characteristics  indicated 

at  f i jlt -  '-',  '..  With  each  of  the  earlier  molts  the  form  approaches  more  and  more 
nearly  the  nymphal  Stage,  which  is  represented  in  its  final  form  at  tig.  •'?.  In 
this  stage  the  prominent  features  are  the  large  wing-pads.  The  general  color  is 
dark  reddish-brown,  with  the  lighter  areas  indicated  in  the  illustration— tlie  eyes 
remaining  a  crimson  color.  In  all  the  preparatory  active  stages  the  insect  is 
:  oval  and  very  much  Battened,  little,  if  at  all,  resembling  the  adult,  but 
rather  some  scale  insect,  and  is  very  sluggish.  The  adult  (fig.  1)  comes  from 
the  last  nymph,  and  is  a  little,  clear-winged  insect ,  closely  resembling  the  Cicada 
or  harvest  By  vastly  reduced.  Like  the  latter,  its  wings  close  roof  wise  in  repose, 
lor  is  reddish-crimson,  with  the  brown  or  black  markings  indicated  in  the 
illustration.  The  last  or  hibernating  brood  turns  uniformly  br-.w  nish  black,  with 
bronzy  eyes  and  dark  wing- veins,  and  was  described  as  a  distinct  species  [Psylla 
simiiltins),  but  has  been  shown  by  Mr.  Slingerland  '  to  be  merely  a  winter  form, 
which  result  is  confirmed  by  breeding  records  at  this  Department. 

The  life   history    of   the  insect   may   be  briefly   summarised    as    follows:  The 
adults  hibernate  in  crevices  in  the  bark  of  pear  trees-  and  emerge  with  the  first 


-Pear-tree    Psylla:  a,   Kgg;    b.  larva. 
Both  greatly  enlarged.    (Original.) 


1  Bui.  14.  Cornell  Agr.  Exp.  Station.  (><•; 

■'iMi  potto. i  trees  in  an  animated  greenhouse  toe  adults  rested  exposed  on  tin-  twlga  ail  winter 
Without  making  any  attempt  at  concealment,  ami  began  ovipositing  early  in  March,  the  tir-t 
maturing  early  In  April.  The  plants  on  which  they  wintered  were,  however.  In  time  of 
leafing,  fully  four  weeks  in  advance  of  those  on  the  ground, 


4 


warm  spring  days,  copulate,  and  begin  the  deposition  of  eggs  before  the  leaves 
have  expanded,  placing  them  singly  or  in  rows  or  bunches  in  creases  of  the 
bark  of  the  twigs,  on  old  leaf  scars  about  terminal  buds,  and  later,  after  the 
leaves  begin  to  unfold,  on  the  leaves  themselves,  as  already  described.  The 
egg-laying  goes  on  during  April,  probably  later  in  the  North  than  as  far  south 
as  Maryland.  The  larva;  hatch  in  from  ten  to  seventeen  days  (from  ten  to 
twelve  days  being  the  ordinary  summer  period),  station  themselves  on  the  leaf 
petioles  and  in  their  axils  on  the  fruit,  but  chiefly  over  the  surface  of  the  leaves. 
The  moment  they  begin  feeding  the  secretion  of  honeydew  commences,  and  in 
a  very  short  while  the  bulk  of  the  liquid  will  be  several  times  that  of  the  insect, 
rapidly  increasing  until  it  forms  a  good-sized  drop.  This,  when  there  are  mil- 
lions to  aid  in  the  work,  soon  becomes  abundant  enough  to  fall  as  a  6hower 
from  the  tree  whenever  it  is  shaken  by  the  wind.  Mr.  Slingerland  shows  that 
there  are  five  molts,  including  the  last  change  from  the  pupa  to  the  adult  insect, 
and  the  life  from  the  laying  of  the  egg  to  the  adult  covers  a  period  of  about 
thirty  days,  the  periods  between  molts  varying  from  three  to  6even  days. 

RECOKD  OF  BROODS  FOR  MARYLAND. 

The    adults  were  very  numerous  July  20  in  Maryland,  frequently  fifteen  or 
twenty  resting  along  the  midrib  of  a  single  leaf.     They  were  depositing  their 

eggs  along  the  midrib  on  the  upper  sur- 
face, and  also  thickly  along  the  serrated 
margin,  but  on  no  other  part  of  the 
leaf.  From  July  31  to  August  3,  when 
again  examined,  the  eggs  were  much 
more  numerous  and  had  been  fre- 
quently deposited  in  small  clusters,  five 
to  eight  together,  along  the  midrib  and 
at  the  margin  of  the  leaves.  Scarcely 
any  of  the  eggs  at  this  time  had  been 
hatched,  at  least  not  more  than  2  to  3 
per  cent,  and  the  adults  were  still  al- 
most as  numerous  as  ever  and  busily 
ovipositing.  This  brood,  which  was 
the  maximum  one  of  the  season,  was 
with  little  doubt  the  third  one  from  the 
hibernating  individuals— a  month  be- 
ing the  normal  period  for  a  generation. 
A  fourth  brood  of  adults  appeared 
about  the  last  of  August,  and  a  fifth 
about  September  1.  In  breeding  cages  over  young  potted  pear  trees  no  diffi- 
culty was  experienced  in  getting  the  fourth  and  fifth  broods  in  large  num- 
bers, but  in  the  orchard  on  the  mature  foliage— prematurely  mature,  from  the 
sapping  of  the  insects — the  fourth  brood  was  very  scanty  in  number,  show- 
ing not  more  than  one  where  there  were  a  thousand  before,  and  this  in  the 
face  of  the  fact  that  more  eggs  had  been  deposited  than  for  any  previous  brood. 
The  further  decrease  with  the  fifth  brood  was  as  marked,  and  the  greatest  diffi- 
culty was  experienced  in  finding  a  single  adult. 

THE    FUTURE   OUTLOOK. 

Judging  from  the  history  of  the  pear-tree  Psylla  in  the  North,  we  may  expect 
that  the  injury  will  be  very  much  less  in  the  future,  even  if  there  is  not  an  entire 
cessation  of  the  trouble  and  a  disappearance  of  the  pest.     The  fact  that  this 
insect  was  imported  into  the  United  States  with  pear  trees  over  sixty  yeai 
and   was   long  since   widely   distributed   throughout  the  pear  districts  of   the 


Pig.  :i.— Pear-tree  Psylla:  Nymph— greatly 
enlarged.     (Original.) 


Northern  Btatea  and  westward  to  the  Mississippi,  end  bu  yet,  during  all  thii 
time,  rarelj  been  reported  aa  Injuriously  abundant,  argnei  thai  the  eonditiona 
'■vor»bl«  <"  '■  are  seldom  met  with,    it.  complete  disappearance  in 

one  orchard,  after  ■  Tear  oi  excessive  abundance,  la  ■  oaae  In  point;  and  the 
multiplication  In  New  York  State  In  1891  wu  followed  the  nezl  pear 
ling  to  Mr.  Blingerlend,  bj  acaroelj  any  injury  in  oompariaon.    T 
tor  the  audden  multiplication  and  quite  aa  sadden  diaappearance  oi  this  pi 
,ll,lu'"lt  to  Pve-     A  ■""■  I  two  or  three  wintera  favorable  to  bibernation 

to  the  unusual  inoreaee,  and  the  resulting  attack  bring*  the  trees 
condition  which  la  probably  prejudicial  to  the  insect.    With  the  later 
summer  brooda,  aa  pointed  oul  above,  the  condition  oi  the  leavea  which  have 
been  seriously  attacked  by  the  earlier  brooda  la  .such  thai  the  insect  becomes 
nuirk.Mll>  leea  abundant  later  in  the  season.    The  green,  aucculenl  foliage  ol  the 


K';;   ',  full  u-rown  larva:-  aevourtw  a 

'S51  '■  ';  '■  a,1"lt  'Meet    9,  hea.l  of  same;  A.  adult,  natural  size.    All  enla 

A.     (Original.) 

young  spring  growth  ia  especially  favorable,  and  when  the  leavea  become  hard- 
ened and  mature,  and  especially  dry  and  innutrition,,  from  havin  ready 
sapped  of  their  vitality,  they  are  distasteful  and  unsmted  to  the  development  of 
the  later  broods. 

The  parasitic  and  predaceoua  insects  also  become  very  efficacious  by  mid- 
summer, and  a  very  interesting  experience  in  the  case  ,,f  the  Maryland  invasion 
will  be  now  noted. 

HA  rURAL   BNSMIS8 

nemy  for  this  insect  among  the  parasitic  and   predaceoua  species  has, 

previous  to  this  year,  been  recorded.     On  my  tirst  visit  t,,  the  Maryland  orchard 

Shown  what  was  taken  to  be  the  egg  oi  the  PsyUa,  which  proved,  however, 

H  the  egg  of  a  common  lacewing  Qy,  Chryaopa  oeulata  Say.    The  mistake 

I  very  natural  one,  for  the  eggs  occurred  in  extraodinary  numbers  throng] 


•> 


UNIVERSITY  OF  FLORIDA 


3  1262  09216  5009 

out  the  orchard.  On  some  trees  nearly  every  leaf  would  have  one  or  two  of  the 
eggs  of  the  Chrysopa  attached  to  it.  Later  nearly  full-grown  larvae  of  Chrysopa 
were  found  on  the  pear  trees,  attacking  and  devouring  the  adult  Psylla  in  a 
very  vigorous  manner  (see  fig.  4,  d),  and  the  young  larva-  were  found  to  feed 
with  great  readiness  on  both  the  eggs  and  the  young  larval  Psyllas.  It  is  a  safe 
estimate  to  say  that  one  lacewing  fly  larva  will  destroy  several  hundred  eggs 
and  larvae  of  the  Psylla,  in  addition  to  the  adults  which  it  will  destroy  in  its 
later  larval  growth.  The  great  abundance  of  the  Chrysopa  eggs  on  the  pear 
trees  makes  it  not  at  all  improbable  that  the  lacewing  fly  has  much  to  do  with 
the  marked  decrease  in  the  later  broods  of  the  Psylla. 

The  predaceous  habits  of  the  lacewing-rly  larvae  are  of  common  record,  and 
their  beneficial  character  is  well  known;  but  in  view  of  the  important  role 
played  by  this  insect  in  the  economy  of  the  Psylla,  its  life  habits  may  be  briefly 
summarized.  The  eggs  (fig.  4,  a),  instead  of  being  deposited  in  rather  numer- 
ously placed  clusters  or  groups;  as  is 
the  case  with  some  other  species,  are 
distributed  almost  invariably  singly  on 
the  leaves,  rarely  two  together  on  the 
same  stalk.  The  young  larva  (fig.  5) 
cuts  off  the  upper  end  of  the  egg  on 
emerging,  and  is  surprisingly  large  in 
comparison  with  the  egg  from  which  it 
issues.  It  is  light  ash-gray  in  color, 
the  head  abnormally  large,  and  the 
body  armed  with  immense  curved  hairs 
or  spines,  which  give  it  rather  a  fero- 
cious appearance  and  undoubtedly 
make  it  seem  to  the  young  Psylla  a  ver- 
itable dragon.  It  crawls  down  the  egg 
stalk  and  begins  immediately  its  active 
search  for  food.  On  approaching  the 
egg  or  young  larval  Psylla,  it  immedi- 
ately grasps  it  between  its  long,  curved, 
mandiblelike  organs,  which  amount  to 
two  sucking  tubes,  between  the  tips  of 
which  the  egg  or  the  young  larva  is  held 
and  rolled  one  way  and  the  other,  as 
between  thumb  and  finger,  the  juicy 
contents  being  in  the  meantime  rapidly 
extracted.  It  is  a  most  interesting  sight 
to  watch  this  little  larva  at  work  and 
to  note  with  what  celerity  it  grasps  the 
young  Psylla,  quickly  extracts  the  juices,  and  casts  aside  the  dry  shell,  the  whole 
operation  frequently  taking  less  than  a  minute. 

The  larva  is  an  extremely  hungry  one  and  is  always  feeding,  and  its  rapidity 
of  growth  is  limited  only  by  the  abundance  of  the  food  supply.  It  eats  anything 
that  comes  in  its  way,  is  totally  fearless,  and  is  also,  unfortunately,  cannibalistic, 
eating  its  own  kind  with  as  great  readiness  as  it  does  any  other  larva.  After 
about  ten  days  the  larva  becomes  full  grown,  and  spins  up  in  the  curl  of  a  leaf 
or  in  any  partial  protection,  constructing  a  delicate,  slightly  oval,  but  nearly 
spherical  silken  cocoon,  which  is  attached  to  the  leaf  by  silken  threads  (fig.  4,  e). 
This  cocoon  is  very  small,  in  comparison  with  both  the  larva  which  spins  it  and 
the  adult  which  emerges  from  it,  and  is  less  than  one-eighth  of  an  inch  in  long- 
?st  diameter.    The  adult  emerges  in  from  ten  to  fourteen  days,  cutting  off  the 


Fig. 


.—Chrysopa  oculata:  Newly-hatched  larva, 
with  under  side  of  head  and  claw  at 
side.    Greatly  enlarged. 


4 


